libstdc++: Optimize is_reference

Instead of defining is_reference in terms of is_[lr]value_reference,
just define it directly.

libstdc++-v3/ChangeLog:

	* include/std/type_traits (is_reference): Make the primary
	template derive from false_type.  Define two partial
	specializations that derive from true_type.

diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
index b83e7257a9f3e5d034d9ec59182676ab08cc9424..94e73eafd2fb23e58e50a1beaffdc0a035c7c6f2 100644 (file)
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -611,8 +611,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   /// is_reference
   template<typename _Tp>
     struct is_reference
-    : public __or_<is_lvalue_reference<_Tp>,
-                   is_rvalue_reference<_Tp>>::type
+    : public false_type
+    { };
+
+  template<typename _Tp>
+    struct is_reference<_Tp&>
+    : public true_type
+    { };
+
+  template<typename _Tp>
+    struct is_reference<_Tp&&>
+    : public true_type
     { };
 
   /// is_arithmetic